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Accurate epidemiological data on common deafness genes are essential to improve the efficiency and to reduce the cost of molecular diagnosis. They may depend on several factors, including a clear delineation of the source of patients being studied. In the present study, we hypothesize that patients with idiopathic sensorineural hearing loss recruited from different sources might reveal discrepancies in the epidemiological results of genetic screening, because patients from different sources might demonstrate distinct clinical or audiologic features and thus result in biased selection of subjects. To elucidate the relative importance of common deafness genes in Taiwanese and to verify our hypothesis, we conducted a prospective project screening mutations in GJB2, SLC26A4 and mitochondrial 12S rRNA gene in a total of 420 Taiwanese families with idiopathic bilateral sensorineural hearing loss, of which 325 families were recruited from hospitals and 95 from hearing rehabilitation facilities. Allele frequencies of common mutations in these three genes and distributions of the corresponding genotypes were then compared between the two groups. The allele frequencies of mutations in SLC26A4, GJB2 and mitochondrial 12S rRNA in the probands of the 420 families were 14.4, 21.7 and 3.8%, respectively. The allele frequency of SLC26A4 mutations in the hospital group was significantly higher than that in the rehabilitation facility group (16.2 vs. 8.4%, chi(2)-test, p < 0.05), whereas no difference in the frequencies of GJB2 mutations and mitochondrial 12S rRNA mutations was found between the two groups. Distributions of probands classified by SLC26A4 genotypes were also different between the two groups (chi(2)-test, p < 0.05). Accordingly, a discrepancy in the genetic screening results might exist between different sources of idiopathic hearing-impaired patients. Further analysis of audiological results and construction of a logistic regression model showed that different audiological features, namely hearing levels and hearing loss patterns, might be responsible for the unequal distributions of mutations and probands between the hospital and rehabilitation facility groups. [ABSTRACT FROM AUTHOR]